Mixed-Mode Resins

Overview

Bio-Rad's mixed-mode chromatography resins offer unique separation properties and unparalleled selectivity and resolution for a variety of molecules. Multimodal chromatography combines the properties of cation exchange media and metal affinity media, often enabling the separation of biomolecules that appear homogeneous using other chromatographic methods. These mixed-mode media can be used at any stage in a purification process from initial capture to final polishing.

Bio-Rad InPlace process-scale chromatography columns are designed for industrial applications with contained filling, packing, unpacking, and cleaning for safe and hygienic column operation. To learn more about Bio-Rad InPlace columns, click on the video.

Slurry valve on Bio-Rad InPlace column. The separated inlet and washing manifolds make it easy and convenient to fill and unload the chromatography media in the contained system and to sanitize the manifold. The valve body allows buffer to pass behind the valve when it is closed.

Ceramic hydroxyapatite requires special consideration during process-scale chromatography packing primarily due to its high specific gravity and rapid settling rate. Ceramic hydroxyapatite media have a bulk density of 0.63 g/ml and a free setting velocity of 35–125 cm/hr for 40 µm and 125–275 cm/hr for 80 µm. Additionally, ceramic hydroxyapatite media are sensitive to mechanical shear, which can fracture the particles and produce fines.

The affinity capture paradigm that dominates industrial IgG purification has proven unsuitable for IgMs because, in most cases, they are affected adversely by harsh elution conditions. The large size of IgMs is also a challenge because it limits the operating conditions and performance of traditional porous-particle-based chromatography media. This article describes how these challenges can be overcome with available technology to develop effective manufacturing procedures for IgM monoclonal antibodies.

Plamid DNA is being used successfully as a gene delivery vector in a variety of clinical application (Smith et al. 1999). Plasmids for gene therapy are usually produced in an E.coli host. One of the technical challenges associated with producing plasmid DNA of gene therapy grade is the removal of contaminants such as bacterial chromosomal DNA, RNA, host proteins, and endotoxin.

Cation exchange occurs when protein amino groups interact ionically with the negatively charged phosphates. The amino groups are similarly repelled by the calcium sites. Binding depends upon the combined effects of these interactions. These ion exchange interactions can be disrupted by adding neutral salts such as sodium chloride or buffering species such as phosphate to the mobile phase. Cation exchange interactions also weaken with increasing pH. Hence, the addition of salt or phosphate, or an increase in pH, can be used to weaken the interaction. Studies with model proteins have demonstrated that anion exchange, which might be expected from interactions of negatively charged surface residues with calcium, does not make a significant contribution.

Calcium affinity occurs via interactions with carboxyl clusters and/or phosphoryl groups on proteins or other molecules (e.g., nucleic acids); these groups are simultaneously repelled by the negative charge of the CHT phosphate groups. The affinity interaction is between 15 and 60 times stronger than ionic interactions alone and, like classical metal-affinity interactions, is not affected by increasing ionic strength using typical elution ions (e.g., chloride). Species binding through calcium affinity may adsorb more strongly as the ionic strength increase due to ionic shielding of the charge repulsion from the CHT phosphate sites. Metal affinity interactions can be dissociated by phosphate in the mobile phase.

Most large proteins bind by a combination of mechanisms:

Dominantly acidic proteins, such as albumin, bind chiefly by metal affinity interactions. Sodium chloride at 1.0 M reduces retention time by approximately 10% in the presence of phosphate gradients, indicating a minor contribution by cation exchange. To elute acidic proteins, phosphate buffers are required.

Dominantly basic proteins, such as IgG, bind chiefly by cation exchange interactions. Sodium chloride reduces retention time in the presence of phosphate gradients, indication a minor contribution by metal-affinity. Basic proteins may be selectively eluted with either phosphate or salts.

Category Products

Nuvia cPrime mixed-mode media is designed for versatile capture and high recovery across a wide range of salt concentrations and pH in process-scale purification processes for biotherapeutic applications.

CHT ceramic hydroxyapatite and Bio-Gel® crystalline hydroxyapatite mixed-mode media, which offer unique selectivities, can be used at any stage in a chromatographic workflow from initial capture to final polishing.

MPC Ceramic Hydroxyfluoroapatite (Ca10(PO4)6(OH)1.5(F)0.5) is a mixed-mode chromatography resin, a composite of hydroxyapatite and fluoroapatite, with unique separation properties and unmatched selectivity and resolution in the purification of biomolecules.

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